Composition resistor with embedded terminal lead head



March 1, 1966 THOMSON 3,238,490

COMPOSITION RESISTOR WITH EMBEDDED TERMINAL LEAD HEAD Filed March 12, 1958 INVENTOR HOMER G.THOMSON ATTORNEYS United States Patent 3,238,490 COMPOSITION RESISTOR WITH EMBEDDED TERMINAL LEAD HEAD Homer G. Thomson, Greenfield, Wis., assignor to Allen- Bradley Company, Milwaukee, Wis., a corporation of Wisconsin Filed Mar. 12, 1958, Ser. No. 720,845 2 Claims. (Cl. 338273) This invention relates to molded composition fixed resistors, as used in radio receiver circuits and other like electronic uses; and more particularly to such a resistor comprising: a body, preferably elongated and cylindrical, said body being made of a moldable insulating material, preferably end-molded; minute conductor particles dis tributed embedded in at least a portion of said material to form a high-resistance conducting path therethrough, preferably longitudinally; and at each end of said resistance path a terminal electrode which comprises a leadwire and an enlarged head, the latter being embedded in the body and in conductive contact with the resistance path.

In the most successful devices of this sort in the prior art, the head is frusto-conical, with the lead-wire integrally attached to the smaller end of the head, this smaller end being wider than the lead-wire, thus forming a shoulder, which shoulder is exposed at or above the surface of the body.

These prior art resistors have proved highly satisfactory in the past. But recently there has arisen a demand for smaller and smaller resistors of this sort. With these smaller resistors, the prior art frusto-conical head and its cooperation with the body of the resistor are not so satisfactory.

As an illustration of this trend to smaller and smaller resistors, it should be noted that there is already a demand for a watt resistor, with a body 0.140 long and 0.067 in diameter, and with lead-wires 0.015" in diameter.

The principal object of the present invention is to devise a more satisfactory head; not only to overcome the disadvantages of the frusto-conical head in the very small sizes, but also to have a better head in even the sizes in which the prior-art frusto-conical head is completely satisfactory.

Another object of the present invention is to provide a head which resists rotation with respect to the body.

Other objects and advantages of the invention will appear in the description which follows.

In the description, reference is made to the accompanying drawings, forming a part hereof, in which there are shown by way of illustration and not of limitation two certain specific forms in which the article of manufacture of the present invention may be embodied.

In the drawings:

FIG. 1 is a greatly enlarged isometric perspective view of an embodiment of the present invention.

FIG. 2 is a longitudinal section of said embodiment, to the same scale.

FIG. 3 is an end view, as seen from the line 3-3 of FIG. 2, to the same scale.

FIG. 4 is an enlarged side view of the head of a terminal electrode, still further enlarged (twice the scale of FIGS. 1 to 3), so as to disclose more clearly the conformation of the head.

FIG. 5 is a side view (to the same scale as FIG. 4) of a modified head, as seen from either side in FIG. 6.

FIG. 6 is a side view of this modified head, as seen from either side in FIG. 5.

ICC

Throughout the description, the same reference numeral is applied to the same member or similar members.

Turning to FIGS. 1 to 4, it will be seen that the resistor of preferred embodiment shown has an elongated circular cylindrical body 11, which comprises an insulating portion 12, surrounding a high resistance conducting path 13.

The insulating material may consist of any suitable thermal-setting insulating composition, such for example as described in the second column of page 2 of United States Patent No. 2,302,564 to George E. Megow and the present inventor.

The material of the resistance path may consist of conductor particles dispersed in an insulating thermalsetting bin-ding, such for example as the resistance material describe-d in said column of said patent.

The two materials 12 and 13 should be bonded integrally.

In extremely small resistors, the entire body may be made of the resistance material. Optionally such a resistor so made, may be insulated by painting with insulating paint, or in any other appropriate manner, such as by being enclosed in an insulating capsule.

At each end of the body, there is :a terminal electrode 14, highly conductive of both electricity and heat, which electrode comprises a lead-wire 16 and an enlarged head 17, the latter being embedded in the body 11 in conductive contact with the resistance path 13. The entire terminal electrode is preferably of copper, or copper cont aining a small portion of silver as described and claimed in the copending application of Eugene C. Ragatz and the present inventor, Serial No. 669,123, filed July 1, 1957, now abandoned, and may be tin-coated or soldercoated if desired.

In spite of the difference of the head 17, as shown and about to be described herein, from the frusto-conical head of the prior art described earlier herein and in the prior patents cited herein, the resistor of the present invention may be made by the process shown and described in Patent No. 2,302,564, cited earlier herein. Or, if the entire body he made of resistor material, as suggested herein for extremely small resistors, the resistor may be made by the process shown and described in United States Patent No. 2,261,916 to George E. Megow and the present inventor. A resistor made by either or both of these two methods may properly be termed end-molded.

Head 17 will now be described. It may be swaged into shape on the end of lead wire 16, and comprises an inner enlarged portion 18, an outer enlarged portion 19, and between the two enlarged portions a constricted portion 21 formed by a groove 22. This constricted portion 21 is preferably of substantially the same diameter as the lead-wire. Inner enlarged portion 18 is preferably of a materially smaller diameter than outer enlarged portion 19.

Now that the head of the present invention has been described in detail, the reasons for its conformation will now be discussed in comparison with the prior-art frustoconical head.

The function of the shoulder, at the juncture of the prior art frusto-cone and the wire-lead, was twofold: (l) to constitute an abutment for the end of the electrodecarrying plunger when forcing the head into the material of the body when molding the body; and (2) to prevent the starting of cracks in the body, as would be likely at the juncture of as small an element as the wire with the body. In connection with item 1, the shoulder should be large enough to so completely close the hole (in the plunger) which contains the lead-wire during molding, as to prevent flash of metal, or of resistance material, or of insulating material.

In the smaller sizes of resistors, the proper performing of these functions calls for a relatively larger shoulder. But there is not room enough in the body for a proportional increase in the entire frusto-cone, so this is one of the reasons for the conformation of head 17 of the present invention.

The military specification of the Department of Defense of the United States applicable to insulated fixed composition resistors, M1LR11B, prescribes the following two rigorous tests:

4.6.14.1 Direct load. Resistance shall be measured as specified in 4.6.2. Resistors shall then be held by one terminal, and the load shall be gradually applied in the direction of the longitudinal axis of the resistor until the applied load reaches pounds. The S-pound pull shall be applied for at least 5 seconds. (See 3.17.1.)

4.6.14.2 Twisting. Following the test specified in 4.6. 14.1, terminals shall be bent through 90 at a point inch from the body of the resistor, with the radius of curvature at the bend approximately 6 inch. The terminals shall be clamped to within i% inch of the bend on the side between the bend and the remaining portion of the lead, away from the body. The body of the resistor shall then be rotated about the original axis of the bent terminal through 360 in alternating directions for five such 360 rotations at the rate of approximately 5 seconds per rotation. Measurements of resistance shall again be made after completion of the test. (See 3.17.2.)

3.17.1 Direct Load. When resistors are tested as specified in 4.6.14.1, resistor terminals shall withstand a pull of 5 pounds without mechanical damage.

3.17.2 Twisting. When resistors are tested as specified in 4.6.14.2, the resistance shall not change in excess of 1 percent or 0.5 ohm, whichever is greater, nor shall there be any evidence of breakage or other mechanical damage.

Customarily the frusto-conical head of the prior art is formed on the end of the lead-wire by a single-stroke punching operation which twists the end of the Wire into a helix in the course of swaging it into frusto-conical shape. First forming a helix is inherent and automatic in single-stroke swaging; whereas there is no tendency to form a helix in the course of multiple-stroke swaging the columnar heads of the present invention. A columnar head is one formed by swaging without twisting that part of the wire or other stem which goes to form the head: in other words a swaged head with no latent helix.

The twisting test tends to unwind the latent helix of the prior art. The direct-load test tends to enhance this effect.

The smaller the resistor, the harder to meet is the directload test. Even bending the wire in the course of installation may loosen the helix. The head of the present invention, having no latent helix, avoids these effects.

Also, because of the wedge-action of the frusto-cone, the direct-load test tends to cause cracks in the body. Contrast the inner enlarged portion 18 of head 17 of the present invention, which without appreciable wedge action, locks under that part of the body which protrudes into groove 22 of the head.

It should be noted that any loosening of the helix, even though so slight as to be unobservable, or any cracks in the resistance path, even though so slight as to be unobservable, are apt to change appreciably the electrical characteristics of the resistor.

Entirely apart from government requirements, the improvements eifected by the present invention in connection with said requirements are significantly important to the quality of the improved resistor.

The reason why the constricted portion 21, defined by groove 22, is preferably at least as thick as lead-wire 16,

is that otherwise it would introduce a point of weakness against pull; and also would reduce the conductance, both electrical and thermal, of the head. But if this constricted portion were appreciably thicker than the lead-wire, this would reduce the locking surface of the head, with no offsetting advantage in the variant under discussion.

One reason for having inner enlarged portion 18 be of a smaller diameter than outer enlarged portion 19 is that this facilitates the insertion of head 17 into body 11. Also this difference in diameter facilitates the flow of the material 13 of the resistance path backward past the periphery of the inner enlarged portion 18 into groove 22 during molding, which in turn tends to prevent the flow of insulating material 12 from pushing some of the resistance material 13 aside from intimate contact with the inner face of the head, thus reducing the planned area of intimate contact.

It is not necessary that the two enlarged portions 18 and 19 of head 17 be in the form of annular lands, nor have a slightly rounded periphery, nor that constricted portion 22 be in the form of an annular groove extending completely around the head, all as shown in FIG. 4.

For example, the head could have the conformation shown in FIGS. 5 and 6, with inner enlarged portion 23 and outer enlarged portion 24 frusto-conical in shape, and with constricted portion 26 defined by two opposite transverse flat grooves 27. Such a head could be formed in any convenient manner, such by swaging an elongated columnar frusto-cone (positioned with its narrow end inwardly, rather than outwardly as in the prior-art, on the end of the terminal electrode), and then pressing this head between two opposed swages to form the two grooves 27.

Such a head as shown in FIGS. 5 and 6 would have the advantage of resisting relative rotation of the head and the body during the twisting test, or during installation, or in use.

The foregoing detailed discussion of the head of the present invention should render evident not only the differences between that head and the best head of the prior art, but also how differently the other elements of the present invention cooperate with the new head than they did with the prior head. The foregoing discussion should also make clear the reasons for these differences.

Now that two embodiments of the invention have been shown and described, and several departures therefrom have been suggested, it is to be understood that the invention is not to be limited to the specific forms or arrangements of parts herein shown and described.

What is claimed is:

1. A molded composition fixed resistor, comprising an integral body, made of moldable insulating material; minute conductor particles distributed throughout at least a portion of said insulating material to form a high-resistance conducting path therethrough; and at each end of said resistance path a terminal electrode, which comprises a lead-wire and an enlarged head, coaxial and integral therewith, the head being intimately embedded in the body in intimate conductive contact with the resistance path portion of said body; wherein each head comprises an inner enlarged portion, an outer enlarged portion, and a constricted portion between the two enlarged portions, the outer face of the outer enlarged portion being exposed through and flush with a face of the body and constituting an outwardly facing shoulder of the terminal electrode; all of the head inwardly from the exposed portion of the head being in intimate supporting contact with the body; wherein the constricted portion of the head is flattened to enable the head to resist turning with respect to the body.

2. A molded composition fixed resistor, comprising an integral body, made of moldable insulating material; minute conductor particles distributed throughout at least a portion of said insulating material to form a high-resistance conducting path therethrough; and at each end of said resistance path a terminal electrode, which comprises a lead-Wire and an enlarged head, coaxial and integral therewith, the head being intimately embedded in the body in intimate conductive contact with the resistance path portion of said body; wherein each head comprises an inner enlarged portion, an outer enlarged portion, and a constricted portion between the two enlarged portions, the outer face of the outer enlarged portion being exposed through and flush with a face of the body and constituting an outwardly facing shoulder of the terminal electrode; all of the head inwardly from the exposed portion of the head being in intimate supporting contact With the body; wherein the head is a f-rusto-cone, the larger end thereof being axially disposed With respect to the lead-Wire and integrally attached to one end thereof, and wherein the transverse lateral grooves.

References Cited by the Examiner UNITED STATES PATENTS Bradley 338331 Steenweg 33866 MegoW et al. 338273 Carington et a1. 338-324 X Kohring 338-260 Patla 338-276 France.

RICHARD M. WOOD, Primary Examiner.

constricted portion of the head is defined by two opposite 15 CLAUDE A. LEROY, NATHANIEL MARMELSTEIN,

RAY K. WINDHAM, Examiners. 

1. A MOLDED COMPOSITION FIXED RESISTOR, COMPRISING AN INTEGRAL BODY, MADE OF MOLDABLE INSULATING MATERIAL; MINUTE CONDUCTOR PARTICLES DISTRIBUTED THROUGHOUT AT LEAST A PORTION OF SAID INSULATING MATERIAL TO FORM A HIGH-RESISTANCE CONDUCTING PATH THERETHROUGH; AND AT EACH END OF SAID RESISTANCE PATH A TERMINAL ELECTRODE, WHICH COMPRISES A LEAD-WIRE AND AN ENLARGED HEAD, COAXIAL AND INTEGRAL THEREWITH, THE HEAD BEING INTIMATELY EMBEDDED IN THE BODY IN INTIMATE CONDUCTIVE CONTACT WITH THE RESISTANCE PATH PORTION OF SAID BODY; WHEREIN EACH HEAD COMPRISES AN INNER ENLARGED PORTION, AN OUTER ENLARGED PORTION, AND A CONSTRICTED PORTION BETWEEN THE TWO ENLARGED PORTIONS, THE OUTER FACE OF THE OUTER ENLARGED PORTION BEING EXPOSED THROUGH AND FLUSH WITH A FACE OF THE BODY AND CONSTITUTING AN OUTWARDLY FACING SHOULDER OF THE TERMINAL ELECTRODE; ALL OF THE HEAD INWARDLY FROM THE EXPOSED PORTION OF THE HEAD BEING IN INTIMATE SUPPORTING CONTACT WITH THE BODY; WHEREIN THE CONSTRICTED PORTIONS OF THE HEAD IS FLATTENED TO ENABLE THE HEAD TO RESIST TURNING WITH RESPECT TO THE BODY. 